From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:56718) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ghHMZ-0007xM-IJ for qemu-devel@nongnu.org; Wed, 09 Jan 2019 12:09:56 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ghHMX-00045k-DN for qemu-devel@nongnu.org; Wed, 09 Jan 2019 12:09:55 -0500 Date: Wed, 9 Jan 2019 18:09:29 +0100 From: Kevin Wolf Message-ID: <20190109170929.GJ4867@localhost.localdomain> References: <20190108194552.45453-1-vsementsov@virtuozzo.com> <20190109112311.GB4867@localhost.localdomain> <5ddd78e0-90ed-a6e5-c454-f1a2e44c1a37@redhat.com> <20190109165111.GI4867@localhost.localdomain> <61f6ac4d-91ab-f9cb-67e5-e0f5ce17524d@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <61f6ac4d-91ab-f9cb-67e5-e0f5ce17524d@redhat.com> Subject: Re: [Qemu-devel] [PATCH] file-posix: add rough-block-status parameter List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org, qemu-block@nongnu.org, armbru@redhat.com, eblake@redhat.com, mreitz@redhat.com, fam@euphon.net, stefanha@redhat.com, den@openvz.org Am 09.01.2019 um 17:55 hat Paolo Bonzini geschrieben: > On 09/01/19 17:51, Kevin Wolf wrote: > > Am 09.01.2019 um 17:42 hat Paolo Bonzini geschrieben: > >> On 09/01/19 12:23, Kevin Wolf wrote: > >>> Also note that this is only metadata preallocation; full preallocation > >>> will still return allocated for the protocol layer and so it will always > >>> be slow. > >> > >> Full preallocation these days can create images with preallocated but > >> known-zero blocks, I think? > > > > That would defeat one of the main purposes of preallocation because it > > would still require COW and metadata updates on the first write. > > Sorry I mean at the protocol level, like FALLOC_FL_ZERO_RANGE. It would > still require metadata updates on the filesystem level, unlike "real" > full preallocation, but no qcow2 metadata updates. preallocation=full doesn't do that. preallocation=falloc is more like it, though that is just posix_fallocate(), not FALLOC_FL_ZERO_RANGE. But when called on a new file, it might result in the same thing? Not sure. Kevin